I need to remove a section of a concrete slab between two floors, 2 x 4 meters of an area that is 5 x 4 meters.
I want the cut in the remaining slab to be straight and even so that the HEA beam that will be placed there fits well.
The easiest would be a concrete saw, but right where the cut should be, there's a wall on top of the slab. So there's no room for a machine from above.
My thought was to chisel everything from above but leave a margin to the intended cut of about 5 cm. Then I rent a handheld power cutter and "cut" down the remaining concrete along the intended cut.
Is it possible to saw a 4-meter long cut from underneath? How quickly can you saw through 10 cm thick concrete with reinforcement?
The concrete is quite easy to chisel, I have tried. It was poured in the 1940s and is a rather porous concrete, but with stones in it.
I want the cut in the remaining slab to be straight and even so that the HEA beam that will be placed there fits well.
The easiest would be a concrete saw, but right where the cut should be, there's a wall on top of the slab. So there's no room for a machine from above.
My thought was to chisel everything from above but leave a margin to the intended cut of about 5 cm. Then I rent a handheld power cutter and "cut" down the remaining concrete along the intended cut.
Is it possible to saw a 4-meter long cut from underneath? How quickly can you saw through 10 cm thick concrete with reinforcement?
The concrete is quite easy to chisel, I have tried. It was poured in the 1940s and is a rather porous concrete, but with stones in it.
Cutting from underneath works well with a power saw and shouldn't take too long (just one cut and nothing falling down?). But make sure to wear a mask and have a good stance to stand on, not fun if it pinches above your head with such a saw. Time spent is surely 1 hour with some short breaks 
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Visibility issues will arise if you do not use a saw for water.
Thanks for the feedback!
I can endure the dust for an hour or two, with a mask and safety goggles. I was afraid I would have to grind for several hours with a 10-kilo machine above my head, phew.
"raster", what is that? I have to work
The room is now concrete-clean, finishes on walls and floors will be put in place later. Doorways will be sealed and taped over. So I'm not afraid of getting it dirty temporarily.
Unfortunately (?) it will probably not be one of the strongest motor saws, but one that runs on electricity. I'm not too keen on running a gasoline-powered one indoors. For example, Hitachi CM 12Y, 2400W. Unless someone says electric-powered ones are hopelessly bad, then I'd have to open all the windows and doors I can find and hold my breath
The machines with water cooling have a simple connection to a regular hose, but do they work upside down?
I can endure the dust for an hour or two, with a mask and safety goggles. I was afraid I would have to grind for several hours with a 10-kilo machine above my head, phew.
"raster", what is that? I have to work
The room is now concrete-clean, finishes on walls and floors will be put in place later. Doorways will be sealed and taped over. So I'm not afraid of getting it dirty temporarily.
Unfortunately (?) it will probably not be one of the strongest motor saws, but one that runs on electricity. I'm not too keen on running a gasoline-powered one indoors. For example, Hitachi CM 12Y, 2400W. Unless someone says electric-powered ones are hopelessly bad, then I'd have to open all the windows and doors I can find and hold my breath
The machines with water cooling have a simple connection to a regular hose, but do they work upside down?